Frequency- and Amplitude-Modulated Narrow-Band Infrared Emitters

ABSTRACT

IR emission devices comprising an array of polaritonic IR emitters arranged on a substrate, where the emitters are coupled to a heater configured to provide heat to one or more of the emitters. When the emitters are heated, they produce an infrared emission that can be polarized and whose spectral emission range, emission wavelength, and/or emission linewidth can be tuned by the polaritonic material used to form the elements of the array and/or by the size and/or shape of the emitters. The IR emission can be modulated by the induction of a strain into a ferroelectric, a change in the crystalline phase of a phase change material and/or by quickly applying and dissipating heat applied to the polaritonic nanostructure. The IR emission can be designed to be hidden in the thermal background so that it can be observed only under the appropriate filtering and/or demodulation conditions.

CROSS-REFERENCE

This application is a Nonprovisional of and claims the benefit ofpriority under 35 U.S.C. §119 based on U.S. Provisional PatentApplication No. 62/288,598 filed on Jan. 29, 2016. The Provisionalapplication and all references cited herein are hereby incorporated byreference into the present disclosure in their entirety.

TECHNICAL FIELD

The present invention relates to imaging, sensing and optical sourcetechnologies based on infrared (IR) emitters, specifically IR emittersfabricated from polaritonic material structures.

BACKGROUND

Infrared (IR) signaling with the aid of night vision and/or thermalimaging technology for detection has provided a means towards relativelycovert free-space signaling and communications applications. Inaddition, IR signaling can serve as a means of free-space communicationswithin the various atmospheric windows, and can denote a change insensor status (e.g. the detection of chemical agent).

However, current approaches use either high-power IR lasers (FIG. 1A) orspectrally broad, highly diffuse emitters (FIG. 1B). As can be seen fromFIG. 1A, in the case of high-power IR lasers, the high power of thelaser produces a high-visibility signal under the appropriate imagingconditions; however such laser-based sources tend to be highlydirectional, such that outside of a narrow cone of angles between thedetector and the source, an optical signal from such a high-power laserwill not be readily observed. The high output power can also cause a“halo” effect whereby the detected signal saturates multiple pixelswashing out part of the image. In addition, such systems have a largepower requirement that limits battery life, making them unsuitable formany field uses.

In the case of diffuse emitters as shown in FIG. 1B, the source may beobserved over a broader range of angles; however, this comes at the costof being spectrally broad and weak in amplitude, making theirobservation outside of close ranges difficult. In addition, because theyare spectrally broad, such emitters may clearly advertise the locationof the source, since they may be observable not only to authorizedobservers having thermal imagers in a specified wavelength range, e.g.,3 μm thermal imagers, but also to anyone having conventional near-IRnight vision goggles. Thus, these sources are very easy to replicate andintercept.

Thus, despite substantial advancements in technology, significant issueswith these applications persist. To ameliorate these issues, newtechnological approaches are required.

Polar dielectric crystals experience an imbalance of the partial ioniccharges of the atomic species in the crystal. For example, in theexemplary silicon carbide polar dielectric illustrated by the blockdiagram in FIG. 2A, a charge imbalance exists between the partialpositive charge “δ+” of the Si ions in the lattice and the partialnegative charge “δ−” of the C ions. The presence of this partial ioniccharge imbalance enables stimulation of surface phonon polaritons(SPhPs) in such polar dielectric materials. In addition, thesub-diffractional confinement of light can be observed using metallicand highly doped semiconductor species (including many of the polardielectric SPhP crystals when a high density of free carriers arepresent), providing similar behavior in the higher frequency regimes. Inthese cases, the incident light couples to free electrons or holes(“carriers”) in the material in a manner illustrated by the blockschematic in FIG. 2B, providing the mechanism for the sub-diffractionalconfinement of light.

Incident light at wavelengths corresponding to frequencies w between thefrequency ω_(TO) of the transverse optic (TO) and the frequency ω_(LO)of the longitudinal optic (LO) phonons of a polar dielectric material,e.g., as shown by 4H—SiC Raman spectrum curve 301 shown in FIG. 3A,induces coherent oscillations of the crystal lattice of the material.Because of the presence of the positive and negative atomic charges δ+and δ−, these oscillations induce a large surface electromagnetic fieldthat causes a normally transparent dielectric to become highlyreflective within this spectral band, referred to as the “Reststrahlen”band, as seen by dashed IR reflectance curve 302 for 4H—SiC shown inFIG. 3A (and also shown in FIG. 3B). See Joshua D. Caldwell, LucasLindsay, Vincenzo Giannini, Igor Vurgaftman, Thomas L. Reinecke, StefanA. Maier and Orest J. Glembocki, “Low-loss, infrared and terahertznanophotonics using surface phonon polaritons,” Nanophotonics 2015; 4:44-68. Correspondingly, the real part of the dielectric function(permittivity) becomes negative, as shown by solid curve 303 shown inFIG. 3B, which enables the confinement of resonant light withinsub-diffractional volumes through the nanostructuring of these polardielectrics or at interfaces and surfaces of such materials.

A plot illustrating the wide range of surface plasmon (NIR to MWIR) andsurface phonon (MWIR to FIR) polariton materials, often referred tocollectively as “polaritonic” materials, is provided in FIG. 4, withstandard plasmonic metals (e.g. silver, gold, aluminum and copper) thatsupport surface plasmons in the ultraviolet and visible and other moreexotic types of polaritons (e.g. exciton polaritons) being omitted forsimplicity; however, one skilled in the art will readily recognize thatthe materials shown in FIG. 4 are merely exemplary and by no meansconstitute an exhaustive and complete list of available polaritonicmaterials.

It was recently demonstrated by researchers that the Naval ResearchLaboratory (NRL) that nanoscale structures fabricated out of siliconcarbide (SiC) and hexagonal boron nitride (hBN) result in spectrallynarrow resonances within the mid-infrared (10.3-12.5 um for SiC; 6.2-7.3um and 12.1-13.2 um for hBN), with resonance linewidths as narrow as 3cm⁻¹, on par with well-defined crystal vibrations. See Joshua D.Caldwell, Orest J. Glembocki, Yan Francescato, Nicholas Sharac, VincenzoGiannini, Francisco J. Bezares, James P. Long, Jeffrey C. Owrutsky, IgorVurgaftman, Joseph G. Tischler, Virginia D. Wheeler, Nabil D. Bassim,Loretta M. Shirey, Richard Kasica, and Stefan A Maier, “Low-Loss,Extreme Subdiffraction Photon Confinement via Silicon Carbide LocalizedSurface Phonon Polariton Resonators,” Nano Lett. 2013, 13, 3690-3697(SiC); and Joshua D. Caldwell, Andrey V. Kretinin, Yiguo Chen, VincenzoGiannini, Michael M. Fogler, Yan Francescato, Chase T. Ellis, Joseph G.Tischler, Colin R. Woods, Alexander J. Giles, Minghui Hong, KenjiWatanabe, Takashi Taniguchi, Stefan A. Maier, and Kostya S. Novoselov,“Sub-diffractional volume-confined polaritons in the natural hyperbolicmaterial hexagonal boron nitride,” NATURE COMMUNICATIONS (2014) 5:5221(hBN). See also U.S. Pat. No. 9,195,052 to Long et al, entitled“Actively Tunable Polar-Dielectric Optical Devices” (Nov. 24, 2015);U.S. Pat. No. 9,244,268 to Long et al., entitled “Actively TunablePolar-Dielectric Optical Devices” (Jan. 26, 2016); U.S. Pat. No.9,274,532 to Long et al., entitled “Actively Tunable Polar-DielectricOptical Devices” (Mar. 1, 2016); and U.S. Patent Application PublicationNo. 2016/0103341 by Long et al.

These nano-scale polaritonic structures, such as the SiC bowtie antennaarrays whose reflectances are illustrated by the plots shown in FIG. 5A,can provide passive polarization- and frequency-selective infraredreflection spectra due to the sub-diffractional resonance modessupported within the nano-scaled structures. In addition, the IRemission spectra of such SiC bowtie antenna arrays at T=350° C. shown inFIG. 5B demonstrate that by heating the structures to modesttemperatures, tailored IR emission can be produced, with the emissionretaining the polarization and narrow spectral bandwidth of theresonances observed in the reflection spectra shown in FIG. 5A. It hasbeen observed within our lab that heating even to small temperaturessuch as 50° C. is sufficient to induce a measurable emission.

This phenomenon was originally demonstrated for SiC micron-scalegratings and microwires. See Jean-Jacques Greffet, Rémi Carminati, KarlJoulain, Jean-Phillipe Mulet, Stéphane Mainguy, and Yong Chen, “Coherentemission of light by thermal sources,” Nature 2002, 416, 61-64; and JonA. Schuller, Thomas Taubner, and Mark L. Brongersma, “Optical antennathermal emitters,” NATURE PHOTONICS, Vol. 3 (November 2009), pp.658-661. If a device comprising a plurality of nano-scale emitters isfabricated on a substrate homogeneous with the nano-scale emitters (e.g.SiC bowties on a SiC substrate), the IR emission from the nano-scaleemitters will be superimposed upon the broadband high reflectivity (lowemission) of the underlying substrate, providing a large opticalcontrast. On the other hand, if the nano-scale structures are fabricated(or grown) on a dissimilar substrate material, the IR emission fromthose structures will be superimposed upon the IR emission of theunderlying substrate and will result in a broad gray-body radiationspectrum with the narrow-band IR emission signature from the nano-scalestructures superimposed thereon.

While the IR emission from localized SPhP resonators discussed in theliterature has primarily focused on SiC structures, see Greffet, supra,and Schuller, supra, in principle, any polar dielectric crystal can beused, provided the Reststrahlen band is in an appropriate frequencyrange for IR emission at the temperature of operation. This is equallyapplicable to surface plasmon polaritons. In the case of the latter,such materials will operate over a broader spectral range, but theresonance linewidths will be significantly broadened with respect to thelower-frequency SPhP materials.

Although use of most plasmonic metals (e.g. gold and silver) would becost-prohibitive and would require excessive temperatures, even inexcess of their melting points, to achieve emission near theirresonances in the visible spectral region, a significant effort has alsobeen focused on developing alternative lower-loss plasmonic materials.For instance, developments from Prof. Jon-Paul Maria's group at NorthCarolina State University have led to a low-loss plasmonic material inthe form of dysprosium-doped cadmium oxide that would offer thepotential for IR emitters in the 2-8 μm range. See E. Sachet, C. T.Shelton, J. S. Harris, B. E. Gaddy, D. L. Irving, S. Curarolo, B. F.Donovan, P. E. Hopkins, P. A. Sharma, A. L. Sharma, J. F. Ihlefeld, S.Franzen, and J.-P. Maria, “Dysprosium-doped cadmium oxide as a gatewaymaterial for mid-infrared plasmonics” Nature Materials 14, 414-420(2015).

Additional materials such as transparent conducting oxides would provideopportunities in the 1-5 um region. See Gururaj V. Naik, Vladimir M.Shalaev, and Alexandra Boltasseva, “Alternative Plasmonic Materials:Beyond Gold and Silver,” Adv. Mater. 2013, 25, 3264-3294. While theoptical losses (efficiency) of these plasmonic materials is higher thanin their phonon polariton counterparts, which will result in broaderemission linewidths, they do offer the potential for tailored IRemitters in a spectral range where currently no known phonon polaritonsexist (λ<6 μm). As noted above, a wide array of these polaritonicmaterials is presented in FIG. 4. It should be noted that all of thosepresented are in various states of commercial maturity, but successfulsynthesis of all has been demonstrated. Further, it should be statedthat this list is not meant to be exhaustive, but that this approach isequally applicable to tailored IR emitters of all kinds, for instanceSPhP, surface plasmon and dielectric resonators.

SUMMARY

This summary is intended to introduce, in simplified form, a selectionof concepts that are further described in the Detailed Description. Thissummary is not intended to identify key or essential features of theclaimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter. Instead, it ismerely presented as a brief overview of the subject matter described andclaimed herein.

The present invention utilizes the properties of polaritonic materialsto provide IR emission devices that can be frequency- and/oramplitude-modulated to provide spectral, temporal and spatial patternsthat can be recognized only under the appropriate filtering and/ordemodulation conditions.

The IR emission devices comprise one or more arrays of fabricatedpolaritonic infrared emitters arranged on a substrate, where the arraysof emitters are coupled to a heater configured to provide heat to one ormore of the emitter arrays in the device. When the fabricated infraredemitters are heated, they produce an infrared emission that can bepolarized and whose spectral emission range, emission wavelength, and/oremission linewidth can be tuned by the material used to form theelements of the array and/or by the size and/or shape of the emitters.

In some embodiments, the nanoscale emitters are formed from or arecoated with a ferroelectric polaritonic material which is used tomodulate the frequency response of the polaritonic IR emitters throughthe application of a piezoelectric strain that changes the material'spolarization state and can be induced by the application of an externalbias.

In other embodiments, the polaritonic IR emitters are formed from or arecoated with a phase change material such as vanadium dioxide (VO₂),vanadium pentoxide (V₂O₅), germanium-antimony-tellurium (GeSbTe), ortungsten trioxide (WO₃), which can change the infrared reflection of theemitters by the application of a thermal, electrical, or optical pulsewhich changes the material from a “metallic” to a “dielectric” state,thereby enabling the amplitude of the emission from the IR emitters tobe modulated.

In other embodiments, the polaritonic IR emitters are coated with athermal dissipation layer such as nanodiamond. Such materials can serveto conduct the heat rapidly away from the emitting material, therefore“shutting off” the IR emission or spectrally tuning the emission energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate aspects of exemplary thermal signalingdevices according to the prior art.

FIGS. 2A and 2B are schematics illustrating aspects of the behavior ofpolar dielectric materials used in an IR emitter in accordance with thepresent disclosure.

FIGS. 3A and 3B are plots illustrating additional aspects of thebehavior of polar dielectric materials used in an IR emitter inaccordance with the present disclosure.

FIG. 4 is a chart illustrating the ranges of resonant frequencies forsurface plasmon (NIR to MWIR) and surface phonon (MWIR to FIR) polaritonmaterials that may be suitable for use in an IR emitter in accordancewith the present disclosure.

FIGS. 5A and 5B are plots illustrating the reflectance (FIG. 5A) and IRemission spectra (FIG. 5B) of antenna arrays formed from SiC bowtienano-scale emitters in accordance with the prior art.

FIGS. 6A-6D illustrate the aspects of the apparent vs. measuredtemperatures of SiC slabs (FIGS. 6A and 6C) and nano-scale emitterarrays (FIGS. 6B and 6D).

FIGS. 7A and 7B are block schematics illustrating a side view (FIG. 7A)and a top view (FIG. 7B) of an IR emitter comprising one or morenano-scale structure arrays in accordance with the present disclosure.

FIGS. 8A-8C illustrate aspects of a polaritonic IR emitter incorporatingferroelectric materials into one or more nano-scale structure arrays inaccordance with the present disclosure.

FIGS. 9A-9D illustrate aspects of a polaritonic IR emitter incorporatingphase change materials into one or more nano-scale structure arrays inaccordance with the present disclosure.

FIGS. 10A-10B are block schematics illustrating aspects of a polaritonicIR emitter incorporating phase change materials into one or morenano-scale structure arrays in accordance with the present disclosure.

DETAILED DESCRIPTION

The aspects and features of the present invention summarized above canbe embodied in various forms. The following description shows, by way ofillustration, combinations and configurations in which the aspects andfeatures can be put into practice. It is understood that the describedaspects, features, and/or embodiments are merely examples, and that oneskilled in the art may utilize other aspects, features, and/orembodiments or make structural and functional modifications withoutdeparting from the scope of the present disclosure.

The present invention utilizes the properties of polaritonic materialsto provide IR emission devices that can be frequency- and/oramplitude-modulated to provide spectral, temporal and spatial patternsthat can be easily recognized under the appropriate filtering and/ordemodulation conditions.

Aspects of the means by which the infrared emission signals can beimaged or detected for potential applications will be described below inthe context of the FIGURES, which form a part of the disclosure of thepresent invention. It will be noted that in the FIGURES and in thedescription herein, where a structural element appears in more than oneFIGURE, those elements are denoted by the same reference numeral, withonly the first digit being changed to reflect the FIGURE in which theyare shown. For example, IR emitter array 700 shown in FIGS. 7A/7Bcorresponds to IR emitter array 800 shown in FIGS. 8A/8B, IR emitterarray 900 shown in FIGS. 9A/9B, and IR emitter array 1100 shown in FIG.11.

As noted above, if a device comprising an array of polaritonicnano-scale structures is fabricated on a substrate homogeneous with thenano-scale structures (e.g. SiC bowties on a SiC substrate), the nanostructure's IR emission will be superimposed upon the broadband highreflectivity (low emission) of the underlying substrate, providing ahigh optical contrast, whereas if the nano-scale structures arefabricated (or grown) on a dissimilar substrate material, the IRemission from those nano-scale structures will be superimposed upon theIR emission of the underlying substrate and will result in a broadgray-body radiation spectrum with the narrow-band IR emission signaturefrom the nano-scale structures superimposed thereon.

This difference in the IR emission of a such a device, depending on thesubstrate on which it is formed, provides a great deal of flexibility inthe design of such IR emission devices, enabling a device to be designedto hide the presence of the signal in a broadband infrared source, toprovide a high degree of contrast relative to the background substrate,or to provide a signal that can only be observed if the nanostructureddevice is illuminated by an external source having a certain frequencyor at high temperatures by an IR imager configured to detect certainfrequencies. In addition, the material and structure of the device canbe tuned to provide more or less thermal contrast vis a vis thesubstrate, thereby permitting the device to be more or less visible asdesired.

FIGS. 6A/6B and 6C/6D illustrate the way in which an array of nano-scalepolaritonic IR emitters can be used to produce a desired thermal image.

FIG. 6A depicts thermal images of a metal chuck and a SiC substrate thathave a measured temperature (as measured by, e.g., a thermocouple) of75° C., and shows that the metal chuck has a thermally imaged “apparent”temperature of 76° C., while the SiC substrate—while having the samemeasured temperature as the chuck—appears to be much cooler, with anapparent temperature of 66° C.; FIG. 6C shows a similar difference inapparent temperatures of a metal chuck and a SiC substrate both having ameasured temperature of 120° C., with the metal chuck having an apparenttemperature of 121° C. and the SiC substrate exhibiting a much coolerapparent temperature of 103° C.

In addition, as shown in FIGS. 6B and 6D, SiC in the form of one or morearrays of nano-scale IR emitters can appear “warmer” to a thermal imagerthan the solid slab of SiC used as a substrate for the array, where allof which exhibit apparent temperatures that are cooler than the measuredtemperature, but range in actual apparent temperatures with variationsdue to spectral shifts in the SPhP resonance frequencies. Thus, as shownin FIG. 6B, a SiC nano-scale structure array having a measuredtemperature of 75° C. has an apparent temperature in the range of about63 to about 65° C., while a SiC nano-scale structure array having ameasured temperature of 120° C. (FIG. 6D) has an apparent temperature inthe range of about 105 to about 109° C. This difference between themeasured and apparent temperatures occurs due to the method by which athermal camera is calibrated. Because a thermal camera determines theapparent temperature based on the total integrated intensity collectedover a spectral bandwidth of the camera and assumes it to be agray-body, mirrors, which do not emit, can appear much cooler than theiractual measured temperature. By making appropriately designed SPhP orSPP nano-scaled structures, one can tailor the apparent temperature ofan object without changing its true measured temperature.

As described in more detail below, in accordance with the presentinvention, the present invention takes advantage of these thermalproperties of polaritonic materials to provide an IR emission devicecomprising arrays of fabricated IR emitters formed from polaritonicmaterials that exhibit phonon or plasmon polariton resonances when theyare heated above room temperature and/or are illuminated by light havingwavelengths within their Reststrahlen band, where the devices can bemodified to provide a desired thermal response. In many embodiments, thepolaritonic IR emitters in devices in accordance with the presentinvention will be in the form of nanoscale emitters such as polaritonicnanoantennas and often will be referred to as such in the descriptionbelow, but one skilled in the art will readily recognize that otherconfigurations of the polaritonic emitters such as one- ortwo-dimensional gratings, meshes, etc., can also be used, and all suchemitter configurations are deemed to be within the scope of the presentdisclosure.

FIGS. 7A and 7B provide a side and a top view, respectively, of anexemplary general configuration of an IR emission device in accordancewith one or more aspects of the present invention.

Thus, as can be seen from FIGS. 7A and 7B, an IR emission device inaccordance with the present invention comprises one or more arrays 700of nanoscale polaritonic IR emitters arranged on a substrate 703, withan intermediate dielectric membrane 702 disposed between the substrate703 and the emitter array to provide mechanical stability and thermalisolation to the heated nanoscale IR emitter arrays to reduce powerconsumption.

The arrays of IR emitters are coupled to a heater 704 that is configuredto provide heat to one or more of the emitter arrays in the device.Boron-doped nanocrystalline diamond is especially suited for use as aheater in an IR emission device in accordance with the present inventionbecause it is optically transparent and will not interfere with thethermal signal from SiC; however, one skilled in the art will recognizethat other heating systems (e.g. serpentine metal resistive heaters) canbe used as appropriate. While omitted from the FIGURE for simplicity, insuch cases, electrical contacts would be utilized to drive a currentthrough the heater.

As described above, when the nanoscale IR emitters are heated by heater704, they produce an IR emission that can be polarized using carefuldesign of the IR emitter structure. In addition, in accordance with thepresent invention, the spectral emission range, emission wavelength,and/or emission linewidth of the IR emission can be tuned by varying theany one or more of the polaritonic material used, the size of theemitters, and/or their shape. In some cases the IR emission of theemitters can be tuned so as to cause the array of emitters to have adifferent “perceived” temperature than that of the underlying substrate.

Thus, in accordance with the present invention, by tailoring thecharacteristics of the device, an IR emission device formed from such apolaritonic material nano-scale structure array can be tailored toprovide a desired IR emission response. For example, by selecting anappropriate material for the substrate and/or the IR emitters, the IRemission from the device can cause the device to have a desired IRemission spectrum that can be used as a tailored optical source orbeacon or can be used to modify the perceived temperature of the devicein a manner as described above. In some embodiments, the device can bedesigned to be “hidden” from view unless the device is illuminated bylight having an appropriate frequency, e.g., a frequency spectrallyclose to the resonance of the nanoscale IR emitters. In otherembodiments, a heater can be configured to apply heat to selected IRemitter arrays or to produce variations in the actual temperaturesapplied to different IR emitter arrays on the same device, therebyproducing a spatially patterned IR emission signature that can identifya source of the IR emitters.

It will be noted here that one skilled in the art will recognize thatthe device design illustrated in FIGS. 7A/7B is merely exemplary, andother designs can be used in implementing the key features of theinvention, i.e., the use of nano-scale structures of nanophotonic andphotonic materials for tailored narrow-band and polarized IR emitterswhich can provide a source of IR emission for a wide range ofapplications and the use of various mechanisms by which the IR emissionfrom the emitters can be frequency- or amplitude-modulated over a widerange of modulation frequencies and modulation depths. In addition,while these features are described primarily in the context of IRemitters that are heated to provide an IR emission, one skilled in theart will recognize that in many cases one or more of these features canalso be used to provide modulated absorption/reflection/transmissionfrom similar devices at ambient temperatures.

One way in which the IR emitters in a device in accordance with thepresent invention can be tuned and/or modulated is through the use ofspecific kinds of emitter materials or coatings on the emitters. Thus,the polaritonic resonances can be tuned by using ferroelectric materials(e.g. lead zirconate titanate), phase change materials (e.g., vanadiumpentoxide or germanium telluride), and/or fast thermal dissipationmaterials (e.g. nanodiamond or boron arsenide) to induce fast changes inthe amplitude or free-space wavelength of the resonances.

As discussed above, any change in the amplitude or wavelengthcorresponding to the resonance frequency will result in a commensuratechange in the IR emission spectrum. As described below, in many cases,these ferroelectric, phase change, or fast thermal dissipation materialscan be used as a coating for multi-layered IR emitters formed frompolaritonic materials. However, many of these phase change andferro/piezoelectric materials are also semiconductors and/or polardielectric materials in their own right and so in some embodiments canbe used in devices where a single material provides both theplasmonic/SPhP-based IR emitter/sensor and the material fortransduction, simultaneously. While we mention only single-material orbi-material iterations of this invention, it should be noted that oneskilled in the art will also recognize that more complicatedmultilayered and/or metamaterial-based structures with variouspolaritonic, ferroelectric, phase change, and/or fast-thermaldissipation materials to achieve these aims within a user-definedfrequency range are also within the scope of this patent.

FIGS. 8A-8C illustrate aspects of an exemplary embodiment of an IRemission device in accordance with the present invention in whichferroelectric materials are used to obtain a frequency-modulated thermalresponse of the polaritonic IR emitters.

As with the embodiment illustrated in FIGS. 7A and 7B described above,in the exemplary embodiment illustrated in FIGS. 8A and 8B, an IRemission device in accordance with the present invention includes anarray 800 of nanoscale polaritonic IR, or thermal, emitters (labeled as“TE” in the FIGURE) arranged on a silicon substrate 803, with anintermediate dielectric membrane 802 disposed between the substrate 803and the emitter array 800.

In the embodiment illustrated in FIG. 8A, each of the individualpolaritonic IR emitters 801 in the array 800 comprises an IR emittercore 801 a formed from a polaritonic material such as silicon carbide(SiC) that is coated with an outer layer 801 b of a ferroelectric (FE)material such as aluminum nitride (AlN) or barium strontium titanate(BST).

In some cases, e.g., AlN or BST, the ferroelectric material is also apolar dielectric capable of supporting phonon polaritons, so that insome embodiments, as shown in FIG. 8B, the ferroelectric material isused to form the IR emitters 801 themselves rather than simply be usedas a coating. In some embodiments, all of the emitters are coated withor formed from the same ferroelectric material, while in otherembodiments, a subset of the emitters can be coated with or formed froma different ferroelectric material so as to produce a spatially varyingstrain, and thus a spatially varying IR emission pattern, e.g., one thatcan identify the owner of the IR emitters to a reader of the thermalsignal. In still other embodiments, one or more of the emitters can beformed from a ferroelectric material core with a coating of a phasechange material; while in other embodiments, one or more of the emitterscan be formed from a phase change material core with a coating of aferroelectric material.

Whether coated with a ferroelectric material or formed from one, theemitters 801 are coupled to a heater 804 that is configured to provideheat to one or more of the emitters in the array so as to produce an IRemission in a manner described above, where the IR emission can serve asa narrow-band infrared optical source or beacon or that may cause theheated array of emitters to have a different “perceived” temperaturethan that of the underlying substrate and/or surrounding environment.

In addition, in this embodiment of an IR emitter in accordance with thepresent invention, the emitters are coupled to electrical contacts 805and a voltage source which can apply a bias across the ferroelectricmaterial. The ideal configuration of the contacts will be dictated bythe IR emitter design and the orientation of the ferroelectric crystalplanes in the device. The voltage source can be any suitable sourcecapable of applying a bias to the device, e.g., a battery or other powerpack.

When a voltage pulse is applied to the coated or solid ferroelectric IRemitters 801, the voltage reorients the spontaneous polarization of theferroelectric material, thereby inducing a strain in the ferroelectriccoating or emitter material. This change in strain modifies thefrequency or frequencies of the optical phonons of the polar dielectricmaterial forming the IR emitters, thus modifying the spectral frequencyof their sub-diffractional resonances.

Thus, in accordance with the present invention, the output frequency ofthe IR emitters as well as their “perceived” temperature can be tuned byselecting an appropriate ferroelectric material to obtain the desiredresponse and/or by choosing an appropriate electrical bias to be appliedto an existing ferroelectric array.

In some embodiments, the polarization of the ferroelectric material canalso be changed through the injection of free carriers (electrons and/orholes) into one or more of the IR emitters or into an area of the IRemission device adjacent to the IR emitters. See U.S. Pat. Nos.9,195,052; 9,244,268; and 9,274,532, supra, and U.S. Patent ApplicationPublication No. 2016/0103341, supra. Such polarization changes can beimplemented in ferroelectric and piezoelectric crystals (e.g. AlN) andmay be induced through electrical, mechanical or thermal stimuli aswell.

This change in polarization of the ferroelectric material enables the IRemission frequency of the nanoscale array to be shifted spectrally asshown in FIG. 8C, where the initial resonance curve 810 a is spectrallyshifted to the position illustrated by curve 810 b through theapplication of a compressive strain via an applied bias to theferroelectric coating or nano-scale structure, while the application ofa tensile strain would induce a spectral shift in the oppositedirection. This spectral shift is transient, and is maintained only aslong as the strain is applied. Therefore, if the strain is applied forshort timescales, for instance sub-microseconds, a frequency modulatedthermal source can be realized. If such a thermal source can be made tohave an apparent temperature similar to that of the local background itwould only be observed if someone demodulates the signal at the correctmodulation frequency.

In other embodiments, use of phase change materials such as vanadiumdioxide (VO₂), vanadium pentoxide (V₂O₅), germanium-antimony-tellurium(GeSbTe), or tungsten trioxide (WO₃), offers another avenue towardsdrastically changing the infrared reflection by the application of athermal, electrical, or optical pulse. FIGS. 9A and 9B illustrateexemplary aspects of IR emission devices in accordance with the presentinvention in which such phase change materials are used to tune thedevice and produce a desired IR emission response.

Thus, as with the previous embodiments described above, in the exemplaryembodiment illustrated in FIGS. 9A and 9B, an IR emission device inaccordance with the present invention includes an array 900 ofindividual nanoscale IR emitters (TE) 901 arranged on a substrate 903,with an intermediate dielectric membrane 902 disposed between thesubstrate 903 and the emitter array. As with the embodiments describedabove, the emitters 901 are coupled to a heater 904 that is configuredto provide heat to one or more of the emitter arrays on a given devicewhen an electrical bias is applied to the heater contacts 905.

In the embodiment illustrated in FIG. 9A, each of the IR emitters 901 inthe array comprises an IR emitter core 901 a formed from a polaritonicmaterial such as silicon carbide that is coated with an intermediatelayer of a dielectric material 901 b and an outer layer 901 c of a phasechange material such as vanadium oxide (VO₂), vanadium pentoxide (V₂O₅),germanium-antimony-tellurium (GeSbTe), or tungsten trioxide (WO₃).Intermediate layer 901 b can thermally isolate the phase change andpolaritonic materials so that they can be held at differenttemperatures; however, the device can also operate without the presenceof this intermediate layer, with the phase change and polaritonicmaterials operating at the same temperature.

In addition, some phase change materials such as vanadium dioxide (VO₂)or vanadium pentoxide (V₂O₅) are also polar dielectric materials capableof supporting SPhPs, so that in some embodiments, as shown in FIG. 9B,the phase change material can be used to form the IR emitters 901themselves rather than merely be used as a coating.

In either case, the IR emitters can be heated by heater 904 to providean IR emission in a manner described above, where the IR emission can beused as a narrow-band infrared source or beacon or may cause the arrayof emitters to have a different “perceived” temperature than that of theunderlying substrate or local environment.

In addition, the phase change material changes properties when the IRemitters are heated. For example, vanadium oxide changes from adielectric i.e., electrically transparent, state to a metallic, i.e.,reflective state. This change in state can also be induced in someembodiments by driving a small current through the phase changematerial, e.g., through electrical contacts 905, while in otherembodiments it can be induced by the use of fast optical laser pulsesapplied to the phase change material.

Thus, as illustrated by the plot in FIG. 9D, in one state, where the IRemitters are at a temperature T above the critical temperature(T>T_(c)), the phase change material has “metallic” properties andbecomes highly reflective and/or absorptive depending on the magnitudeof the imaginary part of the permittivity of the PCM in the metallicstate, such that IR emission from the underlying nano-scale structure issuppressed. In such cases, the IR emission from the devices will bedominated by the IR emission of the metallic phase change material. Ifthe material is a high quality metal, with low loss, it will be highlyreflective with minimal to no IR emission, whereas if it is a poor,lossy metal, it will act as a gray-body and provide a broad IR emission,dictated by its own emissivity, rather than by the underlyingpolaritonic nano-scale structure array.

In a second state, where the IR emitters are at a temperature T lessthan some critical temperature T_(c) (T<T_(c)), the phase changematerial has “dielectric” properties, i.e., is transparent or onlyweakly absorbing, therefore enabling the IR emission from the underlyingnano-scale structures to be transmitted and thus, observed. In such acase, the IR emission will be dictated by the underlying polaritonicnano-scale structure emissivity, and thus will provide the narrow-band,potentially polarized IR emission signature described above.

This change from “metallic” to “dielectric” states is ideal foramplitude modulation. Thus, as illustrated in the plot shown in FIG. 9C,an IR emission device according to this embodiment of the presentinvention can be turned “on” and “off” at a rapid rate, or can beinduced to vary in amplitude to intermediate values depending on thedevice design and the properties of the phase change and polaritonicmaterials used. Such an approach can be quite useful for communicationsusing infrared beacons since the device can be designed so that itsemission(s) has an apparent temperature similar to their surroundingsand will blend into the thermal background, but can be observed clearlyif the observer demodulates the imaged scene at the appropriatefrequency.

The metallic-to-dielectric phase change materials such as vanadiumdioxide (VO₂) are a good candidate for this type of operation. The plotin FIG. 9D illustrates the optical response of a vanadium dioxide filmgrown by atomic-layer epitaxy and shows the change in reflectivity ofthe material depending on whether its temperature T is above or below acritical temperature T_(c), i.e., that it can be in a low-reflectancedielectric state at T<T_(c) and in a high-reflectance metallic state atT>T_(c). Note that large contrasts in the infrared reflectivity can beachieved over a broad spectral range, making VO₂ a particularly suitablematerial for this embodiment. Of course, many other alternative phasechange materials exist, and any suitable material may be used asappropriate.

Other aspects of phase change materials also make them highly suitablefor use in IR emitters in accordance with the present invention. Thephase change exhibited in the entire class of phase change materials isaccompanied by a substantial contrast in refractive index. Large changesin the local refractive index can also be used to induce a spectralshift in the resonance frequency of the sub-diffractional resonator,therefore providing a mechanism towards frequency modulation as well,provided the phase change material still exhibits sufficienttransmission at the wavelength of the IR emission in its metallic state.Phase change materials alternating between crystalline and non-metallicamorphous states would be good candidates for such approaches.

In addition, as with the ferroelectric materials described above, thepolarization of such phase change materials can also be changed throughthe injection of free carriers (electrons and/or holes) into one or moreof the IR emitters or into an area of the IR emission device adjacent tothe IR emitters.

Moreover, in a manner similar to that described above with respect toemitters formed from ferroelectric materials, in some embodiments, allof the emitters are coated with or formed from the same phase changematerial, while in other embodiments, a subset of the emitters can becoated with or formed from a different phase change material so as toproduce a spatially varying change in dielectric function, and thus aspatially varying IR emission pattern, e.g., one that can identify theowner of the IR emitters to a reader of the thermal signal. In stillother embodiments, some of the plurality of emitters in the array can beformed from ferroelectric materials while others are formed from phasechange materials, with their respective IR emission being tuned asdescribed herein so as to provide a predetermined spatially varying IRemission pattern.

In other embodiments, aspects of which are illustrated in FIGS. 10A and10B, the polaritonic IR emitters can be coated with a thermaldissipation layer. In such embodiments, the thermal dissipation layercan serve to conduct the heat rapidly away from the emitting material,therefore “shutting off” the IR emission or spectrally tuning theemission energy. Many of these emitters (e.g. SiC) also exhibit highthermal conductivities, so will naturally lend themselves to fasterthermal cycling.

Thus, as illustrated in FIG. 10A, an IR emission device in accordancewith this embodiment of the present invention includes an array 1000 ofpolaritonic nanoscale IR emitters (TE) 1001 arranged on a substrate1003, with an intermediate dielectric membrane 1002 disposed between thesubstrate 1003 and the emitter array. As with the embodiments describedabove, the emitters 1001 are coupled to a heater 1004 that is configuredto provide heat to one or more of the arrays of emitters on the device.

In addition, in the embodiment illustrated in FIG. 10A, at least some ofthe IR emitters 1001 in the array have an IR emitter core 1001 a formedfrom a polaritonic material that is coated with an outer thermaldissipation layer 1001 b of a thermal dissipation material. Byovercoating the emitters with a high thermal conductivity layer 1001 b,applied heat used to induce the IR emission can be rapidly dissipated,thereby lowering the temperature of the IR emitter nano-scale structure1001 a, which in turn will reduce the amplitude of the IR emission.

In some embodiments, the emitters can be formed from a ferroelectricmaterial or from a phase change material as described above with respectto FIGS. 8B and 9B, respectively, with the emitters then coated with thethermal dissipation layer 1001 b.

In other embodiments, the thermal dissipation layer can be placed as theunderlying dielectric spacer layer 1002 or can be in the form of a viacreated through the backside of the substrate 1003.

Such TDL-based IR emitters provide an ideal approach for amplitudemodulation. Thus, an IR emission device according to this embodiment ofthe present invention can be turned “on” and “off” at a rate asdescribed above in the case of emitters and/or coatings made from phasechange materials, or, as illustrated in the plot shown in FIG. 10B, canbe induced to vary in amplitude to intermediate values depending on thedevice design and the temperature of the IR emitter at any given time.As the IR emitter can be controlled by understanding the interplaybetween the thermal dissipation rate of the TDL and the heat applied tothe IR emitter array, this can serve as a means to modulate theamplitude of the IR emission signature. Such an approach can be quiteuseful for simple signaling with infrared beacons as it can be designedto have an apparent temperature similar to its surroundings and so behidden in the thermal background, but can be observed clearly if theobserver demodulates the imaged scene at the appropriate frequency.

One exemplary TDL material that can be incorporated into an IR emitterin accordance with this embodiment of the present invention would benanocrystalline diamond (NCD), but any other suitable material can beused. Alternatively, as in the embodiments described above with respectto ferroelectric and phase change materials, in some embodiments of anIR emitter having a TDL layer incorporated therein, the nano-scalestructures can be formed from a high thermal conductivity material, forinstance SiC, which can simultaneously serve as both the IR emitter andthe TDL.

While the above device implementations have focused on resonant IRemitters, these modulation approaches can also be used to modulate thethroughput of an optical signal within a waveguide fabricated from apolaritonic material. In such cases, the propagation length andsubdiffractional confinement of polaritonic waveguides is directly tiedto the permittivity of the polaritonic material. By inducing a localstrain through the use of a waveguide fabricated from a polaritonicferroelectric material or from phase change material or a polaritonicwaveguide coated with a ferroelectric or phase change material, thepermittivity of the waveguide material can be modified, thus providingagain a means for modulating the transmitted and/or reflected opticalsignal.

Advantages and New Features

The devices outlined in this disclosure would serve to provide aspectrally narrow, polarized light source that is also semi-diffuse,low-power, light-weight, with minimal electronic and mechanicalcomponents that could induce failure, potentially low-cost and can beamplitude and/or frequency modulated. This provides the benefits of bothwide-viewing angles and long battery life, visibility over long ranges,while also providing spectral and polarization specific behavior withfrequency and/or amplitude modulation of the response that can enablecovert operation and/or modulated optical sources for beacons or opticalcommunications devices. The divergence of the source can in principlealso be tailored by modifying the periodicity of the nano-scalestructure array, the shape of the nano-scale structures, orincorporation of dispersive elements/optics with those structures.

One could envision a large area (mm to cm size scale) single array thatcould be used to provide a spectral signature that could be superimposedupon either the IR emission of a broad band infrared source or the IRemission from the background to hide the signal in plain sight. Anotheralternative would be to fabricate a series of thermally isolated IRemitter arrays that could be individually addressed. This approach wouldalso provide the benefits of the single array design, while alsoproviding the opportunity to create unique spatial patterns that couldbe more readily discerned with imaging technology, albeit with theadditional cost of the more complicated fabrication. Another possiblealternative is to use these sources in conjunction with chemical sensorsor as Surface Enhanced Raman or Surface Enhanced Infrared Absorptionsensors themselves that can emit the covert pattern only when a changeof status occurs (e.g. detection of chemical species of interest).Furthermore, these emitters can provide narrow-band sources of a definedfrequency and polarization that can operate over a broad spectral rangewhere solid-state narrowband sources (LEDs and laser diodes) arecurrently limited or completely absent (MWIR to THz).

These emitters can potentially provide a low-power, low-cost, polarizedIR source where commercial sources are not currently available (λ>13 um)and/or for gas-phase sensing.

The modulated signal could be used for many potential signaling orcommunications applications. For example, an array of nanoscale IRemitters in accordance with the present invention can be arranged in apredetermined pattern to provide an identifying signal that is visibleonly to someone having appropriate imaging and filtering equipment. Inother embodiments, the modulated emission(s) source could be used toidentify sensors that have had a change of status (e.g. a chemicalsensor detecting a dangerous gas) or to perform chemical spectralanalysis. Or in another embodiment, the devices could be worn or held bypersonnel and be used for communications or to identify the personnel asbeing of a specific origin or belonging to an authorized organization.

They could also serve as an alternative, modulated, solid-state infraredlight source with narrow spectral band, polarized emission wherebydepending on the polaritonic material chosen (e.g. plasmonic or phononpolariton species) the emission wavelength could be designed anywherefrom the near-infrared (e.g. highly doped transparent conductingoxides), into the MWIR (e.g. dysprosium doped cadmium oxide) into theLWIR (e.g. silicon carbide and III-Nitrides) and FIR (e.g. phosphide-,antimonide-, arsenide- and telluride-based semiconductors).

Finally, these emitters are also strong absorbers of light on resonance,and highly reflective off-resonance and therefore can be used as apassive device that when illuminated by an external light source or bythe thermal energy of the local environment can provide a similarnarrow-band and polarized response, but in this case could be coverteven in areas where minimal background emission is anticipated. Theseand other applications derived from these modulated IR emitters alsobenefit from the atmospheric windows (e.g. the 3-5 and 8-12 μm windows,denoted by gray cross-hatched regions in FIG. 4), whereby light withthese wavelengths can be transmitted over long distances with minimalabsorption or scattering of light within the atmosphere.

Alternatives

Many additional uses in both the military and commercials spheres couldbe realized from this invention. Such modulated thermal sources could beused for molecular sensing, as the basis for free space communications,as on-chip sources for infrared nanophotonic devices or lab-on-a-chipapproaches or for spectroscopy.

Although particular embodiments, aspects, and features have beendescribed and illustrated, one skilled in the art would readilyappreciate that the invention described herein is not limited to onlythose embodiments, aspects, and features but also contemplates any andall modifications and alternative embodiments that are within the spiritand scope of the underlying invention described and claimed herein. Thepresent application contemplates any and all modifications within thespirit and scope of the underlying invention described and claimedherein, and all such modifications and alternative embodiments aredeemed to be within the scope and spirit of the present disclosure.

What is claimed is:
 1. An infrared (IR) emission device, comprising: aplurality of fabricated nano-scale polaritonic material structuresarranged on a substrate, the polaritonic material structures comprisingat least one ferroelectric material; an electrical power sourceconfigured to induce a strain in the ferroelectric material; and aheater configured to apply heat to at least one of the polaritonicmaterial structures; wherein heat from the heater causes the at leastone polaritonic material structure to produce an IR emission; andwherein a predetermined wavelength, a predetermined linewidth, or apredetermined amplitude of the IR emission from the at least onepolaritonic material structure can be obtained by an application of apredetermined electrical bias from the electrical power source to theferroelectric material.
 2. The IR emission device according to claim 1,wherein the at least one polaritonic material structure is formed from apolaritonic core having a ferroelectric material coating thereon.
 3. TheIR emission device according to claim 2, wherein the polaritonic core issilicon carbide (SiC) and the ferroelectric material coating is aluminumnitride (AlN).
 4. The IR emission device according to claim 1, whereinthe at least one polaritonic material structure is formed from apolaritonic ferroelectric material.
 5. The IR emission device accordingto claim 4, wherein the polaritonic ferrorelectric material is AN orbarium strontanate.
 6. The IR emission device according to claim 4,wherein at least some of the polaritonic material structures are coatedwith a thermal dissipation layer.
 7. The IR emission device according toclaim 1, wherein the array of fabricated nano-scale polaritonic materialstructures comprises an array of silicon carbide bowtie nanoantennas. 8.The IR emission device according to claim 1, further comprising athermal dissipation layer disposed between the substrate and thepolaritonic material structures.
 9. The IR emission device according toclaim 1, wherein the heater comprises boron-doped nanocrystallinediamond.
 10. An infrared (IR) emission device, comprising: a pluralityof fabricated nano-scale polaritonic material structures arranged on asubstrate, the one polaritonic material structures comprising at leastone phase change material; and a heater configured to apply heat to atleast one of the polaritonic material structures; wherein heat from theheater causes the at least one polaritonic material structure to producean IR emission; and wherein a predetermined wavelength, a predeterminedlinewidth, or a predetermined amplitude of the IR emission from the atleast one polaritonic material structure can be obtained by changing thelocal dielectric function of the phase change material in apredetermined manner.
 11. The IR emission device according to claim 10,wherein the local dielectric function of the phase change material ischanged by a predetermined heating of at least one of the polaritonicmaterial structures.
 12. The IR emission device according to claim 10,wherein the local dielectric function of the phase change material ischanged by a predetermined laser excitation of at least one of thepolaritonic material structures.
 13. The IR emission device according toclaim 10, further comprising a voltage source configured to apply anelectrical bias to the at least one of the phase change materialstructures; wherein the local dielectric function of the phase changematerial is changed by an application of a predetermined voltage bias tothe phase change material.
 14. The IR emission device according to claim10, wherein the at least one polaritonic material structure is formedfrom a polaritonic core having a phase change material coating thereon.15. The IR emission device according to claim 14, wherein thepolaritonic core is silicon carbide (SiC) and the phase change materialis vanadium oxide (VO₂), vanadium pentoxide (V₂O₅),germanium-antimony-tellurium (GeSbTe), or tungsten trioxide (WO₃). 16.The IR emission device according to claim 10, wherein the at least onepolaritonic material structure is formed from a polaritonic phase changematerial.
 17. The IR emission device according to claim 16, wherein thepolaritonic phase change material is vanadium dioxide (VO₂) or vanadiumpentoxide (V₂O₅).
 18. The IR emission device according to claim 16,wherein at least some of the polaritonic material structures are coatedwith a thermal dissipation layer.
 19. The IR emission device accordingto claim 10, wherein the array of fabricated nano-scale polaritonicmaterial structures comprises an array of silicon carbide bowtienanoantennas.
 20. The IR emission device according to claim 10, furthercomprising a thermal dissipation layer disposed between the substrateand the polaritonic material structures.
 21. The IR emission deviceaccording to claim 10, wherein the heater comprises boron-dopednanocrystalline diamond.
 22. An infrared (IR) emission device,comprising: a plurality of fabricated nano-scale polaritonic materialstructures arranged on a substrate, at least some of the polaritonicmaterial structures being coated with a thermal dissipation materiallayer; and a heater configured to apply heat to at least one of thepolaritonic material structures; wherein heat from the heater causes theat least one polaritonic material structure to produce an IR emission;and wherein a predetermined amplitude, a predetermined wavelength, or apredetermined linewidth of the IR emission from the at least onepolaritonic material structure can be obtained by selectively applyingheat to and removing heat from the at least one polaritonic materialstructure.
 23. The IR emission device according to claim 22, wherein thethermal dissipation layer is nanodiamond or boron arsenide.
 24. The IRemission device according to claim 22, wherein the heater is boron-dopednanocrystalline diamond.
 25. An infrared (IR) emission device,comprising: a plurality of fabricated polaritonic material structuresarranged on a thermal dissipation layer; and a heater configured toapply heat to at least one of the polaritonic material structures;wherein heat from the heater causes the at least one polaritonicmaterial structure to produce an IR emission; and wherein at least oneof a predetermined amplitude, a predetermined wavelength, and apredetermined linewidth of the IR emission can be obtained byselectively applying heat to and removing heat from the at least onepolaritonic material structure.
 26. The IR emission device according toclaim 25, wherein the thermal dissipation layer is nanodiamond or boronarsenide.
 27. The IR emission device according to claim 25, wherein theheater is boron-doped nanocrystalline diamond.
 28. An infrared (IR)emission device, comprising: a first plurality of fabricated nano-scalefirst polaritonic material structures arranged on a substrate, the firstpolaritonic material structures comprising at least one ferroelectricmaterial; and a second plurality of fabricated nano-scale secondpolaritonic material structures arranged on the substrate, the secondpolaritonic material structures comprising at least one phase changematerial; an electrical power source configured to induce a strain inthe ferroelectric material; and a heater configured to apply heat to atleast one of the first and second polaritonic material structures;wherein heat from the heater causes the at least one polaritonicmaterial structure to produce an IR emission; and wherein apredetermined spatially varying wavelength, a linewidth, or amplitude ofthe IR emission can be obtained by an application of a predeterminedelectrical bias from the electrical power source to a predeterminedplurality of the first and/or second polaritonic material structures.29. The IR emission device according to claim 28, further wherein thewavelength, linewidth, or amplitude of the second polaritonic materialstructures is changed by a predetermined heating of the secondpolaritonic material structures.
 30. The IR emission device according toclaim 28 wherein the wavelength, linewidth, or amplitude of the secondpolaritonic material structures is changed by a predetermined laserexcitation of at least one of the polaritonic material structures.